Motors in the form of a Permanent Magnet Synchronous Machine (PMSM) are gradually replacing classic DC motor drives as well as other AC motor drives in a large number of industrial and domestic applications. This is due, at least in part, on increasingly stringent specifications on energy consumption with a view to sustainable development that tend to place other motor drives at a disadvantage with respect to PMSM drives. Those skilled in the art recognize a number of advantages with respect to the key features of a permanent magnet motor such as compactness, efficiency, power factor, robustness and reliability. Notwithstanding those advantages, a known drawback with respect to controlling such a motor is that a vector controlled PMSM drive needs to use an encoder or a resolver for correctly aligning the stator current vector (i.e., correctly detecting rotor position). Such an electromechanical position transducer is not typically present in low cost/low power DC motor drives or constant V/Hz induction motor drives. The inclusion of such a transducer presents a significant disadvantage to the adoption of a PMSM drive for use in low cost/low power applications.
The performance of sensorless PMSM drives depends on torque control capabilities as well as on position and speed estimation accuracy and bandwidth. There is accordingly a need in the art for a sensorless PMSM drive capable of operation at any speed (including low and zero speed) which includes functionality for making both initial and incremental rotor position detections.